(Noun-Verb) - To run directly into your offensive lineman's rear end so violently that it in turn causes the quarterback to misplace the pigskin out of his hands and onto the ground ultimately causing a fumble.

To completely fuck-up in your profession. A butt fumble (n) or to butt fumble (v).

Example 1: Did you see Mark Sanchez, the Jets quarterback, run into the ass of his own lineman and lose the football? That butt fumble has been voted the worst of the worst sports mistakes for two months straight now.

When a shart goes beyond conventional means. A solid clump of poo that is not recoverable by a clench of the buttocks requires a unique set of variables at play. The fart needs to have enough force to propel the fecal clump fast enough to escape the clench reaction of your standard shart. The clump itself has to be hard enough so it can then further damage your reputation by enlisting the aid of gravity and visibly appearing at the bottom of your pantaloons (if loosely fitting of course). An added variable, but not required, is that said fecal matter fall out of your pants all together, making you want to take a similar route off of a bridge or tall building.

Billy decided it a good idea to pass gas in karate class while in the ready stance, but instantly realize he had committed a butt fumble. He was further humiliated when the turd landed on the dojo floor. Master Rubie was thoroughly discussed and scalded him by saying, "You gross little boy! Go wipe your ass and clean up my floor!".